This invention relates to a one-way clutch used in driving units such as paper feed units of printers and copiers.
Typical conventional one-way clutches used in office machines such as printers and copiers comprise an outer race formed with a plurality of pockets in the radially inner surface thereof so as to be circumferentially spaced apart from each other. Cam surfaces are formed on the radially outer surfaces of the respective pockets. The cam surfaces are inclined in the same circumferential direction to define wedge-shaped spaces having a wedge angle in the respective pockets. In each pocket, a roller and a spring biasing the roller toward the narrow end of the wedge-shaped pocket are received. The outer race is received in a cylindrical casing having an open end and a closed opposite end with the open end closed by a lid (as disclosed in JP Patent Publication 3270667B).
A shaft extends through the lid, the outer race and the closed end of the casing, and is supported by the radially inner surface of the outer race. When the shaft rotates toward the narrow ends of the respective wedge-shaped spaces, the rollers are wedged into the narrow ends of the respective wedge-shaped pockets, thereby transmitting torque from the shaft to the outer race and the casing. When the shaft rotates in the opposite direction, the rollers move toward the wide ends of the respective wedge-shaped pockets, thereby disengaging the shaft from the outer race, allowing free rotation of the shaft.
When the shaft rotates toward the narrow ends of the respective wedge-shaped pockets, the rollers abut against and are wedged between the respective cam surfaces and the outer periphery of the shaft, thereby locking the clutch. When the rollers abut against the cam surfaces and the outer periphery of the shaft, impulsive pushing force is produced which tends to radially outwardly displace the portions of the outer race located radially outwardly of the respective cam surfaces and also radially inwardly press the outer periphery of the shaft.
But since the outer race is fitted in the casing of the one-way clutch without play to ensure rigidity of the clutch, the portions of the outer race located radially outwardly of the cam surfaces can be scarcely displaced radially outwardly, which in turn makes it difficult to effectively reduce (absorb) the impulsive pushing force applied from the rollers.
The pushing force is thus almost entirely applied to the outer periphery of the shaft. Because this one-way clutch is used in office machines, the shaft is ordinarily not hardened and is thus low in hardness. Thus, when impulsive pushing force is applied to the shaft, impressions and/or fretting wear tend to develop on the outer periphery of the shaft. If such wear progresses, gaps may develop between the respective rollers and the outer periphery of the shaft when the clutch is locked, thereby making it difficult to keep the clutch locked.
An object of the present invention is to minimize wear of the shaft by the rollers when the clutch is locked.